In 3GPP (3rd Generation Partnership Project) LTE (Long Term Evolution) Release 8 and Release 9 specifications, each downlink subframe includes 14 OFDM (Orthogonal Frequency Division Multiplexing) symbols within a control area and a data area. The data area is carried by a PDSCH (Physical Downlink Shared Channel). The first one to four OFDM symbols of each subframe are corresponding to the control area. The control area includes a PCFICH (Physical Control Format Indicator Channel), a PDCCH (Physical Downlink Control Channel), a PHICH (Physical HARQ Indicator Channel), CRSs (Cell-specific Reference Signal) and some blank REs (Resource Element). DCI (Downlink Control Information) carried in the PDCCH includes resource allocation information and other control information of one or more UEs. Generally, one subframe may include a plurality of PDCCHs, each PDCCH corresponding to a different UE.
PDCCH includes UL Grant (Uplink Grant) PDCCH and DL Grant (Downlink Grant) PDCCH. Each PDCCH may be dispersed over the entire system bandwidth and all the OFDM symbols corresponding to the control area. In accordance with channel conditions corresponding to the UEs, the DL Grant PDCCH may occupy 1, 2, 4 or 8 CCEs (Control Channel Element) adaptively, and each CCE includes 36 REs. For example, for the UEs with a well channel condition, the DL Grant PDCCH may occupy 1 or 2 CCEs, and for the UEs with a bad channel condition, the DL Grant PDCCH may occupy 4 or 8 CCEs. To be specific, the number of CCEs occupied by the DL Grant PDCCH is mainly determined by PDCCH link adaption, and such a procedure mainly comprises: receiving, by a base station, a wideband CQI (Channel Quality Indicator) of a corresponding data area reported by the UE; determining, by the base station, an SINR (Signal to Interference plus Noise Ratio) corresponding to the CQI in accordance with the wideband CQI reported by the UE; and determining, by the base station, the number of CCEs occupied by the DL Grant PDCCH allocated to the UE in accordance with the SINR. The PDCCH link adaptation finishes at this point.
Through the above process, the base station can determine the number of CCEs allocated to the DL Grant PDCCH of the UE in accordance with the wideband CQI of the corresponding data area reported by the UE. However, the transmission mode adopted by the control area is different from that adopted by the data area. Usually, the control area adopts a transmission mode of 2*2 SFBC (Space Frequency Block Code), while the data area adopts eight transmission modes, i.e., Transmission Mode 1 to Transmission Mode 8. Moreover, the inter-cell interference on a transmission signal over the control area is also different from that over the data area. The wideband CQI of the corresponding data area of the base station reported by the UE can merely reflect the channel quality of the data area rather than the channel quality of the control area, so that the number of CEEs allocated by the base station to the DL Grant PDCCH of the UE is of low accuracy. As a result, it is unable to realize the PDCCH link adaptation accurately and to ensure reliability of the DL Grant PDCCH transmission.